U.S. patent application number 09/034746 was filed with the patent office on 2001-10-25 for table saw with switched reluctance motor.
Invention is credited to BEAN, FREDERICK R., BREWER, KEVIN D., CEROLL, WARREN A., GEHRET, ROBERT S., KENYON, MARIA I., O'BANION, MICHAEL L., PARKS, JAMES R., PORTER, DAVID A., PUZIO, DANIEL.
Application Number | 20010032534 09/034746 |
Document ID | / |
Family ID | 27366487 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010032534 |
Kind Code |
A1 |
CEROLL, WARREN A. ; et
al. |
October 25, 2001 |
TABLE SAW WITH SWITCHED RELUCTANCE MOTOR
Abstract
A machine tool has a work table which defines a working surface
and has a cutting tool which is attached to and movable with
respect to the work table. The position of the cutting tool with
respect to the working surface is controlled by a mechanism which
elevates the cutting tool with respect to the working surface and
angulates the cutting tool with respect to the working surface. The
cutting tool is mounted to a support plate which is pivotably
attached to the work table. The elevating mechanism includes a
threaded rod and a nut which engages a pivoting link. The pivoting
link also engages the cutting tool. Rotation of the threaded rod
pivots the link which in turn raises and lowers the cutting tool. A
spring biases the cutting tool towards its lower position to remove
play between the components. The angulating mechanism includes a
lever, two cams and a locking rod. Rotation of the lever moves the
locking rod longitudinally due to the action between the two cams.
The longitudinal movement of the rod compresses the support plate
between the work table and a bracket to maintain the position of
the support plate with respect to the work table. Also included is
an integral arbor wrench which is accessible when the throat plate
is removed to lock the arbor to facilitate tool changing. The
wrench is designed to not allow reassembling of the throat plate
when the wrench is in engagement with the arbor shaft.
Inventors: |
CEROLL, WARREN A.; (OWING
MILLS, MD) ; BEAN, FREDERICK R.; (FINKSBURG, MD)
; KENYON, MARIA I.; (TANEYTOWN, MD) ; PARKS, JAMES
R.; (TIMONIUM, MD) ; GEHRET, ROBERT S.;
(HAMPSTEAD, MD) ; PORTER, DAVID A.; (HANOVER,
PA) ; O'BANION, MICHAEL L.; (WESTMINISTER, MD)
; PUZIO, DANIEL; (BALTIMORE, MD) ; BREWER, KEVIN
D.; (MOUNT JOY, PA) |
Correspondence
Address: |
ADAM AYALA
THE BLACK & DECKER CORPORATION
701 EAST JOPPA ROAD-TW199
TOWSON
MD
21286
|
Family ID: |
27366487 |
Appl. No.: |
09/034746 |
Filed: |
March 4, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09034746 |
Mar 4, 1998 |
|
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08663538 |
Jun 17, 1996 |
|
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5875698 |
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60044459 |
Apr 29, 1997 |
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60058521 |
Sep 11, 1997 |
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Current U.S.
Class: |
83/473 ;
83/477.1; 83/481; 83/491 |
Current CPC
Class: |
Y10T 83/7705 20150401;
B27B 5/38 20130101; B23D 45/068 20130101; Y10T 83/7793 20150401;
Y10T 83/7747 20150401; B23D 47/12 20130101; Y10T 83/7726
20150401 |
Class at
Publication: |
83/473 ;
83/477.1; 83/481; 83/491 |
International
Class: |
B27B 005/24 |
Claims
What is claimed is:
1. A machine tool comprising: a work table defining a work surface;
a cutting tool attached to and movable with respect to said work
table; and a switched reluctance motor driving the cutting
tool.
2. The machine tool of claim 1, further comprising: a mechanism for
positioning said cutting tool relative to said working surface of
said work table, said mechanism comprising: a support plate
pivotably secured to said work table, said cutting tool being
mounted to said support plate to move between a first position
where said cutting tool extends through an aperture in said work
table and a second position where said cutting tool is positioned
below said working surface; a cutting tool angulating mechanism
mounted to said support plate, said angulating mechanism being
operable to pivot said support plate with respect to said work
table such that said cutting tool angulates with respect to said
working surface; and a cutting tool elevating mechanism mounted to
said support plate, said elevating mechanism being operable to move
said cutting tool between said first and said second positions.
3. The machine tool according to claim 2 wherein said support plate
pivots about an axis which is located on said working surface.
4. The machine tool according to claim 2 further comprising at
least one pivot quadrant for pivotably securing said support plate
to said work table.
5. The machine tool according to claim 4 wherein said pivot
quadrant comprises: a support bracket attached to said work table;
a pivot bracket pivotably attached to said support bracket and
fixably attached to said support plate; and a retaining strap
attached to said support bracket, said retaining strap engaging
said pivot bracket to maintain attachment of said pivot bracket to
said support bracket.
6. The machine tool according to claim 2 wherein said angulating
mechanism comprises: a locking rod extending between a front side
and a rear side of said support plate; a bracket attached to said
work table and positioned adjacent to said rear side of said
support plate, said locking rod extending through said bracket; a
locking arm attached to said locking rod and movable between a
first position and a second position, said support plate being free
to pivot relative to said work table when said locking arm is in
said first position, said support plate being compressed between
said bracket and said work table to prohibit pivoting of said
support plate when said locking arm is in said second position.
7. The machine tool according to claim 6 further comprising a
bearing block cam attached to said support plate and a locking arm
cam attached to said locking arm, said locking arm cam cooperating
with said bearing block cam when said locking arm is moved from
said first position to said second position to compress said
support plate.
8. The machine tool according to claim 7 further comprising a
biasing member disposed between said support plate and said locking
arm, said biasing member urging said locking arm in a direction
which urges said locking arm into contact with said support plate
to create a clearance between said bearing block cam and said
locking arm cam and to create a clearance between said bracket and
said support plate.
9. The machine tool according to claim 6 wherein, said work table
includes at least one adjustable stop, said adjustable stop
including a cam rotatably secured to said work table, said cam
being selectively locked to said work table in a plurality of
positions to adjustably limit thee pivoting of said support
plate.
10. The machine tool according to claim 2 wherein said elevating
mechanism comprises: an adjustment screw rotatably secured to said
support plate; an adjustment nut threadably engaging said
adjustment screw such that rotation of said adjustment screw
operates to move said adjustment nut longitudinally along said
adjustment screw; and a pivot link pivotably secured to said
support plate, said pivot link extending between said adjustment
nut and said cutting tool such that rotation of said adjustment
screw operates to pivot said pivot link to move said cutting tool
between said first and said second positions.
11. The machine tool according to claim 10 further comprising a
biasing member for urging said cutting tool into one of said first
and second positions.
12. The machine tool according to claim 10 further comprising means
for resisting rotation of said adjustment screw.
13. The machine tool according to claim 12 wherein, said means for
resisting comprises a washer attached to said adjustment screw and
a biasing member for urging said washer against said support plate
to provide frictional resistance to rotation of said adjustment
screw.
14. The machine tool according to claim 2 wherein, said cutting
tool comprises: a gear case mounted to said support plate; a motor
attached to one end of said gear case; an arbor shaft rotatably
secured to a second end of said gear case; and a cutting device
attached to said arbor shaft.
15. The machine tool according to claim 14 wherein, said gear case
is biased against a face of said support plate.
16. The machine tool according to claim 14 further comprising: a
lever pivotably attached to said gear case and movable between a
first position and a second position; a wrench pivotably attached
to said lever, said wrench adapted to engage said arbor shaft to
prevent its rotation with respect to said gear case when said lever
is in said first position, said arbor shaft being free to rotate
when said lever is in said second position.
17. The machine tool according to claim 16 wherein, said work table
includes a throat plate disposed within a cavity defined by said
work table and extending through said work surface, said throat
plate defining said aperture in said work table, said throat plate
being prevented from being properly disposed within said cavity
when said lever is in said first position.
18. The machine tool according to claim 2 wherein, said cutting
tool is biased against a face of said support plate.
19. The machine tool according to claim 2 wherein, said work table
includes at least one adjustable stop, said adjustable stop
including a cam rotatably secured to said work table, said cam
being selectively locked to said work table in a plurality of
positions to adjustably limit the pivoting of said support
plate.
20. The machine tool according to claim 1, wherein the motor drives
a arbor shaft, the cutting tool being drivingly connected to the
arbor shaft, and the arbor shaft having multiple threads.
21. The machine tools according to claim 20, wherein the arbor
shaft has a double thread.
22. A machine tool comprising: a work table defining a work
surface; an arbor shaft having multiple threads; a cutting tool
rotatingly driven by the arbor shaft and movable with respect to
said work table; and a motor driving the arbor shaft.
23. The machine tools of claim 22, wherein the arbor shaft has a
double thread.
24. The machine tool of claim 23, further comprising: a mechanism
for positioning said cutting tool relative to said working surface
of said work table, said mechanism comprising: a support plate
pivotably secured to said work table, said cutting tool being
mounted to said support plate to move between a first position
where said cutting tool extends through an aperture in said work
table and a second position where said cutting tool is positioned
below said working surface; a cutting tool angulating mechanism
mounted to said support plate, said angulating mechanism being
operable to pivot said support plate with respect to said work
table such that said cutting tool angulates with respect to said
working surface; and a cutting tool elevating mechanism mounted to
said support plate, said elevating mechanism being operable to move
said cutting tool between said first and said second positions.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is based upon and claims priority
under 35 USC .sctn. 119 and 37 CFR .sctn. 1.78 of copending U.S.
provisional applications Ser. No. 60/044,459, filed on Apr. 29,
1997, and Ser. No. 60/058,521, filed on Sep. 11, 1997. The present
application is also a continuation-in-part of U.S. application Ser.
No. 08/663,538, filed on Jun. 17, 1996.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a table saw with a switched
reluctance motor, and more particularly, to a table saw with a
switched reluctance motor having a variable speed and automatic
braking for operating a rotatably mounted saw blade.
[0003] Most prior art table saws use universal motors and gear or
belt reduction drives to power a rotatably mounted saw blade. For
turning the universal motor on and off in a convenient manner, a
switch is utilized. Recent models of prior art table saws may also
employ a brake to shorten the coast downtime of a rotatably mounted
saw blade. This is accomplished by reconnecting the universal motor
into a short circuited generator. This is sometimes referred to as
"regenerative" braking or "dynamic" braking. A separate circuit
operated by a second contact of the switch engages and disengages
the brake. Unfortunately, the optimum brush timing, or "brush
lead," is different for a motor and a generator. Thus, braking the
motor in the manner described above increases wear and tear on the
motor brush and commutator. In addition, the braking action of a
universal motor decreases sharply as the motor slows down,
increasing the total stopping time.
[0004] As will be seen in the discussion that follows, the present
invention employs a switched reluctance motor which eliminates the
aforementioned problems associated with universal motors,
particularly those that employ regenerative or dynamic braking.
SUMMARY OF THE INVENTION
[0005] The object of the present invention is achieved by providing
a table saw having a table, a frame supporting that table, a
rotatably mounted saw blade mounted under the table, a switched
reluctance motor to said saw blade for rotatable powered operation
thereof about its rotatable mounting, and drive circuit for
controlling the operation of the switched reluctance motor.
[0006] Other aspects and advantages of the invention will become
apparent from the description and claims which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The accompanying drawings illustrate preferred embodiments
of the invention according to the practical application of the
principles thereof, and in which:
[0008] FIG. 1 is a perspective view of a table saw in accordance
with the present invention;
[0009] FIG. 2 is a cutaway perspective view of the table saw shown
in FIG. 1;
[0010] FIG. 3 is a cut-away perspective view similar to FIG. 2 with
the motor, saw blade and gear case removed to illustrate the
angular adjustment mechanism;
[0011] FIG. 4 is an exploded perspective view of the angular
adjustment mechanism shown in FIG. 3;
[0012] FIG. 5 is a side view of the support plate shown in FIGS.
1-3 with the motor, saw blade and mounting plate included to
illustrate the height adjustment mechanism;
[0013] FIG. 6 is an end view of the height adjustment mechanism
shown in FIG. 5;
[0014] FIG. 7 is an exploded perspective view of the pivot
quadrants incorporated into the angular adjustment mechanism;
[0015] FIG. 8 is a schematic cross-sectional view taken through the
gear case illustrating the assembly of the gear case to the support
plate;
[0016] FIG. 9 is an exploded perspective view of the height
adjustment mechanism shown in FIGS. 5-6;
[0017] FIG. 10 is a side view illustrating the arbor locking
mechanism in the unlocked position;
[0018] FIG. 11 is a side view similar to FIG. 10 but showing the
locking mechanism in the locked position;
[0019] FIG. 12 is a side view schematically illustrating an
adjustment mechanism for the bevel adjustment system; and
[0020] FIG. 13 is a block diagram of a control circuit for
operating a switched reluctance motor that drives the rotatably
mounted saw blade.
DETAILED DESCRIPTION
[0021] Referring now to the drawings in which like reference
numerals designate like or corresponding parts throughout the
several views, there is shown in FIG. 1 a table saw which is
designated generally by the reference numeral 10 incorporating a
switched reluctance motor in accordance with the present invention.
Table saw 10 comprises a base 12 which supports a generally
rectangular work table 14 defining a working surface 16. Work table
14 includes a throat plate 18 which includes an elongated slot 23
through which a circular saw blade 22 protrudes. Saw blade 22 is
capable to being adjusted for angularity with respect to working
surface 16 by an angular bevel adjustment mechanism 24 as well as
being capable for being adjusted for depth of cut by a height
adjustment mechanism 26.
[0022] Referring now to FIG. 2, table saw 10 is illustrated with
working surface 16 of work table 14 partially removed and a portion
of base 12 cutaway. Circular saw blade 22 is rotated by a motor 28
which power saw blade 22 through a gear case 30. Bevel adjustment
mechanism 24 adjusts the angular position of saw blade 22 by
pivoting saw blade 22, motor 28 and gear case 30. Height adjustment
mechanism 26 adjusts the cutting depth of saw blade 22 by
longitudinal movement of saw blade 22, motor 28 and gear case 30.
Persons skilled in the art will recognize that other means for
adjusting the height and the bevel of the blade assembly can be
achieved using different means. As discussed above, the motor 28
has typically been a universal motor that is connected to a belt or
gear reduction drive for driving the rotatably mounted saw blade
22. The present invention employs a switched reluctance motor as
the motor 28 in the table saw 10.
[0023] Referring now to FIGS. 2 and 3, bevel adjustment mechanism
24 comprises a pair of pivot quadrants 32, a support plate 34, and
a locking system 36. Each pivot quadrant 32 is attached to a
plurality of bosses 38 extending from the bottom of work table 14
using a plurality of bolts 40. Each pivot quadrant 32 is designed
to pivot around a center which is located on working surface 16 of
work table 14 coincident with the plane of saw blade 22. Thus, the
axis for pivoting support plate 34 lies on working surface 16 and
extends through the plane of saw blade 22 when saw blade 22 is
generally perpendicular with working surface 16. As shown in FIG.
7, pivot quadrant 32 is comprised of a support bracket 42, a pivot
bracket 44 and a retaining strap 46. Support bracket 42 is an
L-shaped bracket which defines a plurality of holes 48 to
facilitate the attachment of pivot quadrant 32 to work table 14 on
one leg of the L. The opposite leg of the L defines an arcuate slot
50 which controls the pivotal movement of pivot bracket 44 and
locates the center of the pivoting at working surface 16 of work
table 14. Pivot bracket 44 extends between support bracket 42 and
support plate 34 and defines a plurality of holes 52 at one end to
facilitate the attachment of support plate 34. The opposite end of
pivot bracket 44 defines a stamped arcuate protrusion 54 which
mates with slot 50 to control the pivoting of pivot bracket 44.
Protrusion 54 is formed out of the material of pivot bracket 44 and
this forming operation defines an arcuate slot 56 once protrusion
54 has been formed. Retaining strap 46 extends across pivot bracket
44 and is attached to support bracket 42 to maintain the engagement
of protrusion 54 with slot 50. Retaining strap 46 defines a formed
protrusion 58 which extends into slot 56 to both guide the pivotal
movement of pivot bracket 44 and to act as a stop to limit the
pivotal movement of pivot bracket 44.
[0024] Referring now to FIGS. 3 and 4, support plate 34 is a
shallow drawn plate which is attached to pivot quadrants 32.
Support plate 34 is designed to support both height adjustment
mechanism 26 and locking system 36. Locking system 36 comprises a
bearing block 60, a locking rod 62, a locking arm 64, a bearing
block cam 66, a locking arm cam 68 and a return spring 70. Bearing
block 60 is a curved member which is attached to a bracket 72 which
is in turn attached to support plate 34. Bearing block 60 thus
pivots with support plate 34 and bearing block 60 extends through
an arcuate slot 74 in the front face of base 12. While the pivotal
movement of support plate 34 moves bearing block 60 within slot 74,
it should be understood that the movement of support plate 34 is
controlled by pivot quadrants 32 and that a clearance will always
exist between bearing block 60 and slot 74.
[0025] Locking rod 62 extends across support plate 34 and through
bracket 72 and bearing block 60 in the front of support plate 34
and through a bracket 76 and a bracket 78 located at the rear of
support plate 34. Bracket 76 is attached to support plate 34 and
defines an aperture for accepting and guiding locking rod 62.
Bracket 78 is attached to work table 14 and it defines an arcuate
slot 80 which accepts locking rod 62 and allows for the pivotal
movement of support plate 34. While the pivotal movement of support
plate 34 moves locking rod 62 within slot 80, it should be
understood that the movement of support plate 34 is controlled by
pivot quadrants 32 and that a clearance will always exist between
locking rod 62 and slot 80. Once locking rod 62 has been inserted
through brackets 76 and 78, a washer 82 and a nut 84 are assembled
to locking rod 62 to provide adjustment for locking system 34. The
front end of locking rod 62 extends through bearing block 60 and
through a D-shaped embossment 86 which is an integral part of
bearing block 60. Locking arm 64 is assembled over the end of
locking rod 62 and secured to locking rod 62 using a hardened
washer 88, a thrust bearing 90, a hardened washer 92 and a nut 94
threadingly received on locking rod 62 as shown in FIG. 4.
[0026] Bearing block cam 66 and locking arm cam 68 are disposed
between locking arm 64 and bearing block 60. D-shaped embossment 86
extends from bearing block 60 through slot 74 in the front face of
base 12. Bearing block cam 66 includes a D-shaped aperture which
mates with embossment 86 and cam 66 is positioned such that the
front face of base 12 is sandwiched between bearing block 60 and
bearing block cam 66. The engagement of the D-shaped aperture of
cam 66 with D-shaped embossment 86 prohibits the rotational
movement of cam 66 with respect to bearing block 60. The face of
cam 66 opposite to the front surface of base 12 defines a camming
surface 96 which reacts with locking arm cam 68 to activate locking
system 34.
[0027] Locking arm 64 defines a D-shaped embossment 98 which mates
with a D-shaped aperture extending through locking arm cam 68 such
that locking arm cam 68 pivots with locking arm 64 when locking arm
64 pivots on locking rod 62. The face of cam 68 opposite to locking
arm 64 defines a camming surface 100 which mates with camming
surface 96 on cam 66 such that pivoting motion of locking arm 64
with respect to locking rod 62 will cause longitudinal movement of
locking rod 62 to activate locking system 36. Return spring 70 is
disposed on locking rod 62 between an ear 102 formed on locking rod
62 and bearing block 60 in order to urge locking rod 62 towards the
rear of base 12 or towards bracket 78. Locking rod 62 is shown with
an additional ear 102 on the opposite side of return spring 70 to
capture spring 70 in the unassembled condition of locking rod 62.
The additional ear 102 requires that the aperture in bearing block
60 which accepts locking rod 62 be provided with a slot (not shown)
to accept the additional ear 102. In this arrangement, the
engagement of the additional ear 102 with the slot in bearing block
60 will prohibit any rotational movement of locking rod 62.
[0028] When camming surface 96 is aligned with camming surface 100,
pivoting of support plate 34 and thus saw blade 22 and motor 28 is
permitted. The biasing of locking rod 62 towards the rear of base
12 causes embossment 98 to bottom against embossment 86. In this
condition, there is a clearance created between camming surface 96
and camming surface 100 as well as a clearance created between
bracket 76 and bracket 78. These clearances allow for a smooth
pivoting of support plate 34 and thus a smooth angular adjustment
for saw blade 22. The pivoting of support plate 34 is controlled by
pivot quadrants 32 while bearing block 60 moves within slot 74 in
the front face of base 12 and locking rod 62 moves within slot 80
in bracket 78. When the desired angle of saw blade 22 is obtained,
locking system 36 is activated by pivoting locking arm 64 on
locking rod 62 which rotates cam 68 with respect to cam 66. Camming
surface 100 is cammed away from camming surface 96 causing
longitudinal movement of locking rod 62. The longitudinal movement
of locking rod 62 compresses support plate 34 between bracket 78
and the front face of base 12 due to washer 82 and nut 84 engaging
bracket 78 and bearing block cam 66 engaging the front surface of
base 12. The flexibility of locking rod 62 due to a center off-set
area 104 and the flexibility of bracket 78 permit the compression
of support plate 34. The adjustment for locking system 36 is
provided for by nut 84.
[0029] Referring now to FIGS. 2, 5, 6 and 9, height adjustment
mechanism 26 comprises a pivot link 110, a biasing spring 112, a
follower nut 114, a height adjustment screw 116 and a crank handle
118 which function to move saw blade 22, motor 28 and gear case 30
longitudinally with respect to support plate 34.
[0030] Support plate 34 defines a generally rectangular opening 120
within which gear case 30 is located. Located adjacent to and
extending generally the entire length of opening 120 are a pair of
formed ribs 122 which provide stiffness to support plate 34. Gear
case 30 includes a housing 124 disposed on one side of support
plate 34 and a cover 126 disposed on the opposite side of support
plate 34. Cover 126 is secured to housing 124 by a plurality of
bolts 128 such that support plate 34 is sandwiched between cover
126 and housing 124. Gear case 30 includes a pair of longitudinally
extending surfaces 130 which engage the opposing sides of opening
120 to guide the movement of gear case 30 within opening 120. Motor
28 is attached to housing 124 and includes an armature shaft 132
having a pinion 134 which meshes with an output gear 136 which is
rotatably supported within gear case 30. The output gear includes
an arbor shaft 138 which provides for the attachment of saw blade
22. Thus, when motor 28 is powered, armature shaft 132 and pinion
134 rotate which rotates output gear 136 and arbor shaft 138 which
in turn rotates saw blade 22.
[0031] In the prior art, single thread screws have been used for
the arbor shaft 138. However, because of the repeated high loads
applied to the blade 22 when cutting, the arbor nut 184 and washers
180 and 182 may be dragged rotationally in a self-tightening
direction. This could make removal of the arbor nut 184 difficult.
A prior art solution includes using a double "D" to lock washer 180
or washer 182 to the arbor shaft 138 to prevent dragging, and
self-tightening, of the arbor nut 184. This solution requires
additional hardware parts or additional machining operations, thus
raising manufacturing costs.
[0032] Accordingly, it is preferable that the arbor shaft 138 have
a twin lead thread, or double thread. As such, the angle of the
threads relative to a plane perpendicular to the shaft axis, or
alpha angle, in the double thread shaft is larger than the alpha
angle in the single thread shaft. The larger alpha angle helps
reduce the torque applied on the arbor nut 184, diminishing its
self-tightening. For example, if the double thread shaft's alpha
angle is twice that of a single thread shaft's alpha angle, the
torque applied on the double-threaded arbor nut would be about half
of the torque applied on the single-threaded arbor nut. Such
reduction of torque minimizes the arbor nut's self-tightening.
Persons skilled in the art will recognize that this result can also
be achieved so long as multiple threads, i.e., triple, quadrupule,
etc., threads, are used on the arbor shaft.
[0033] The alpha angle should be at least 3.degree. and preferably
in a range between 5.degree. and 5.4.degree.. Such range provides a
small screw pitch that prevents a thin blade from falling into the
space between the threads. Otherwise, the blade would fall into the
space between the threads, making the blade eccentric relative to
the shaft, causing excess vibration and poor cut characteristics,
especially at the normal operating speeds of about 4000 RPM.
[0034] The increased alpha angle solution is also advantageous as
it can be implemented with any kind of thread shape. In other
words, the thread cross-sectional shape can be triangular
(V-shaped), round (arcuate), trapezoidal, square, etc. Preferably,
the thread used in the arbor shaft 138 substantially square and is
commonly known as the "ACME thread".
[0035] Referring now to FIG. 8, the accurate positioning of saw
blade 22 is required in order to provide accurate cuts. In order to
accurately position saw blade 22, the front face, or the face
adjacent saw blade 22, of support plate 34 is defined as a datum
face. Cover 126 is provided with a plurality of accurately machines
pads 140 which accurately position cover 126 and thus saw blade 22
with respect to support plate 34. Machine pads 140 are biased
against the datum face on support plate 34 by a plurality of
elastomeric springs 142 each of which is disposed within an
aperture 144 defined by housing 124. A low friction wear pad 146 is
disposed between each elastomeric spring 142 and support plate 34
to facilitate the movement of gear case 30 within opening 120.
Thus, gear case 30, motor 28 and saw blade 22 move longitudinally
within opening 120 guided by surfaces 130 with gear case 30 being
biased against the datum face of support plate 34 by elastomeric
springs 142. As shown in FIGS. 2 and 5, cover 126 includes an
extension 148 which can be utilized for supporting a splitter
and/or guard mechanism for table saw 10 if desired The mounting of
the splitter and/or guard mechanism on cover 126 allows the
components to travel with saw blade 22 during cutting depth and/or
angular adjustments.
[0036] Referring back to FIGS. 2,5,6 and 9, pivot link 110 is
pivotably secured to support plate 34 by an appropriate fastener
150. One arm of pivot link 110 defines a slot 152 which engages a
pin 154 attached to gear case 30. The second arm of pivot link 110
defines a slot 156 which engages follower nut 114. Biasing spring
112 is a tension spring positioned around fastener 150 and is
disposed between pivot link 110 and a retainer 158. Retainer 158 is
attached to follower nut 114 and biasing spring 112 is positioned
such that its spring force biases gear case 30 towards a downward
position. By biasing pivot link 110 in this direction, the play
between the various components of height adjustment mechanism 26
can be eliminated. In addition, the biasing load provided by
biasing spring 112 is resisted by follower nut 114 and not by
adjustment screw 116 as in many prior art table saws.
[0037] Height adjustment screw 116 is rotatably secured at one end
by a bracket 160 which is a separate component or bracket 160 can
be formed out of support plate 34. A nylon bushing 162 is disposed
between screw 116 and bracket 160 to facilitate the rotation of
screw 116 and provide a smoothness of operation. The loading and
thus the wear between screw 116, bushing 162 and bracket 160 is
significantly reduced due to the reaction of spring 112 occurring
through follower nut 114 and not through screw 116. The opposite
end of adjustment screw 116 extends through and is rotatably
supported by bearing block 60. The portion of adjustment screw 116
which extends beyond bearing block 60 is adapted for securing crank
handle 118 to adjustment screw 116 such that rotation of crank
handle 118 causes rotation of adjustment screw 116. Disposed
between bearing block 60 and bracket 72 of support plate 34 is a
hardened washer 164, a powdered metal washer 166, a spring thrust
washer 168 and a hardened washer 170. Powdered metal washer 166 is
secured to adjustment screw 116 by press fitting or other means
known in the art. The biasing of spring thrust washer 168 produces
frictional resistance to the rotation of adjustment screw 116
allowing for the accurate positioning of saw blade 22 and the
ability of height adjustment mechanism 26 to maintain the position
of saw blade 22 during the cutting operation. The frictional
resistance or drag produced by spring thrust washer 168 maintains
the position of adjustment screw 116 and is not affected by the
vibration produced by motor 28 and/or the cutting operation. In
addition, the biasing produced by spring thrust washer 168 removes
any play which may exist between the various components of height
adjustment 26.
[0038] Follower nut 114 is threadingly received on a threaded
portion 172 of screw 116 which is located between bracket 160 and
bearing block 60. Follower nut 114 includes a cylindrical finger
174 which extends into retainer 158, into slot 156 of pivot link
110 and into a slot 176 located in support plate 34 to cause the
pivoting of pivot link 110 by follower nut 114. Slot 176 in support
plate 34 prohibits rotation of follower nut 114 and tends to guide
follower nut 114 as it moves along screw 116. In addition, the
contact between finger 174 and the edge of slot 176 provides the
reaction point for spring 112. Thus, when crank handle 118 is
rotated, adjustment screw 116 is rotated which causes follower nut
114 to move longitudinally along threaded portion 172 of adjustment
screw 116. The direction of movement of follower nut 114 will be
determined by the design of threaded portion 172 and the direction
of rotation of crank handle 118. The longitudinal movement of
follower nut 114 causes pivotal movement of pivot link 110 due to
the engagement of finger 174 which engages slot 156. The pivotal
movement of pivot link 110 causes the longitudinal movement of gear
case 30, motor 28 and saw blade 22 due to the engagement of slot
152 with pin 154. The longitudinal movement of gear case 30, motor
28 and saw blade 22 sets the height of saw blade 22 extending
through work table 14 and thus the depth of cut.
[0039] Referring to FIGS. 8, 10 and 11, cover 126 of gear case 30
supports another unique feature for machine tool 10. One of the
problems associated with machine tools is the changing of the
cutting tool. Saw blade 22 is assembled to arbor shaft 138 and is
frictionally held in position by a pair of washers 180, 182 and an
arbor nut 184. Arbor shaft 138 includes a pair of flats 186 which
accept a wrench (not shown) in order to stop arbor shaft 138 from
rotating when arbor nut 184 is to be loosened or tightened during
the changing of saw blade 22. The wrench for engaging flats 186 is
normally a separate piece which is easily misplaced which then
leads to the wedging of a block of wood or other material against
saw blade 22 to hold arbor shaft 138. The wedging of the block
against saw blade 22 is both dangerous and leads to unnecessary
loading of the bearings supporting arbor shaft 138. The present
invention includes a lever 188 which is pivotably secured to cover
126. A wrench 190 is pivotably secured to lever 188 and moves
within a pocket 192 formed by a ridge 194 which is an integral part
of cover 126 between an unlocked position shown in FIG. 10 and a
locked position shown in FIG. 11. A spring 196 biases wrench 190
into its unlocked position.
[0040] The unlocked position of wrench 190 is shown in FIG. 10
where wrench 190 is disconnected from flats 186 and arbor shaft 138
is free to rotate. The locked position is shown in FIG. 11 where
wrench 190 engages flats 186 to prohibit rotation of arbor shaft
138. The end of wrench 190 engages ridge 194 at both the front of
wrench 190 adjacent arbor shaft 138 to provide support for wrench
190 in the locked position and at the rear of wrench 190 adjacent
to lever 188 to provide support to counteract the torque being
allied to arbor nut 184. Lever 188 is accessible to the operator of
table saw 10 through the opening in work table 14 which accepts
throat plate 18. Lever 188 is designed to extend into the throat
plate opening of work table 14 when wrench 190 is in the locked
position and saw blade 22 is in its full upward position as shown
in FIG. 11 to prohibit the assembly of throat plate 18 with work
table 14 while wrench 190 is in the locked position. Once wrench
190 is moved to its unlocked position, lever 188 will be removed
from the throat plate opening in work table 14 and throat plate 18
can be assembled to work table 14.
[0041] FIG. 12 illustrates a bevel angle stop system for bevel
adjustment mechanism 24. An adjustment cam 200 is attached to the
front panel of work table 14 at opposite ends of slot 74. A
protrusion 202 is formed at both ends of bearing block 60. When saw
blade 22 is positioned at a point perpendicular to working surface
16, adjustment cam 200 at the zero degree position is rotated until
it contacts the zero degree protrusion 202 on bearing block 60.
Adjustment cam 200 is tightened in position using a bolt 204 to set
the zero degree position of saw blade 22. The tightening of bolt
204 has a tendency to rotate cam 200 in a clockwise direction. The
rotation of cam 200 in a clockwise direction urges cam 200 into
contact with protrusion 202 due to the external spiral shape of cam
200 to provide an accurate positioning of the bevel angle for saw
blade 22. The perpendicularity of saw blade 22 can be set by a
square or other means known well in the art. In a similar manner,
the 45.degree. position of saw blade 22 with respect to working
surface 16 can be set by a similar adjustment and locking of
adjustment cam 200 located on the opposite side of slot 74.
[0042] As shown in FIG. 13, a schematic control circuit is
illustrated showing the switched reluctance motor 28 electrically
connected to the electronic motor drive 29 and operated by the
switch 300 in the base 12 of the table saw 10. Switched reluctance
motors rely upon semiconductor switches and complex logic for
operation. Such motors are also capable of braking, again relying
upon those same semiconductor switches and logic.
[0043] As in prior art table saws, the switch 300 may include first
and second contacts. Thus, upon depression of the switch 300, the
switched reluctance motor 28 is energized to drive the rotatably
mounted saw blade 22. Upon release of the switch 300, the second
contact can be electrically connected to the electronic motor drive
370 to brake the switched reluctance motor 28. This will be similar
to the present practice. However, unlike the universal motors,
switched reluctance motors can be controlled to provide braking
down to near zero speed, thus reducing total stopping time.
[0044] Alternatively, the electronic motor drive 370 can be
configured to sense that the switch 300 is open, in other words,
released, and then automatically brake the switched reluctance
motor 28. Thus, the electronic motor drive 370 can be configured in
any desired manner to work in conjunction with the switch 30 to
brake the switched reluctance motor 28.
[0045] Other variations are possible including the addition of a
variable speed control to the switched reluctance motor 28. Another
variation can include a soft start, i.e., relatively slow ramp up
of motor speed, in the electronic motor drive 370 in order to
reduce the strain on a gear reduction drive as well as reduce the
starting in rush current to the switched reluctance motor 28. This
is an advantage when long extension cords are used.
[0046] From the foregoing, it will now be appreciated that the
table saw with switched reluctance motor eliminates wear and tear
on brushes and commutators as in prior art universal motors as well
as regenerative or dynamic braking associated with the universal
motor. Wear and tear is substantially eliminated because switched
reluctance motors rely upon semiconductor switches and complex
logic to operate. Because switched reluctance motors are capable of
braking, as a result of the semiconductor switches and logic, they
can be controlled to provide braking down to near zero speed, thus
reducing the total stopping time.
[0047] Persons skilled in the art may recognize all of the
alternatives to the means disclosed herein. However, all these
additions and/or alterations are considered to be equivalents of
the present invention.
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